The present invention relates to a method as defined in the preamble of claim 1 for extinguishing a fire in a space, especially in a tunnel or equivalent, in which method an extinguishing medium is sprayed in the space by means of spraying heads.
The invention also relates to a fire extinguishing apparatus as defined in the preamble of claim 11.
In recent times, the question of firefighting in tunnels, such as road and railway tunnels and equivalent, has emerged. Several destructive fires have occurred in tunnels because they generally have no permanent fire extinguishing systems. The traditionally imaginable fire extinguishing systems are either sprinkler systems or zonewise triggered spraying systems. In sprinkler systems, the sprinklers are triggered individually by the action of heat. In a tunnel application, they involve the problem that, as a consequence of the fast propagation of hot gases, a very large number of them are triggered even far away from the actual place of fire. Therefore, the pump sizes and correspondingly the pipe sizes should be designed for such a large area that the system would become practically unfeasible. In a zonewise triggered system, the tunnel is divided into zones, and when a signal based on fire detection is received from a zone, the entire zone is triggered. A problem with these systems is how to locate the right zone. Due to the fast propagation of smoke and heat, signals may be received from numerous wrong zones, and again the practical problems of sizing are encountered. Therefore, a special area of investigation in recent times has been the development of new and accurate detection systems.
A problem with all traditional solutions is the difficulty of directing the extinguishing power of automatic firefighting equipment to the right area, i.e. to the area on fire. In tunnels there is always a strong air current, either due to natural ventilation or—more generally—produced by mechanical ventilation. The hot combustion gases rise up and are quickly drifted in the tunnel away from the actual area on fire. Therefore, individual heat-activated sprinklers of conventional sprinkler systems are triggered in a very large area. The capacity of the extinguishing system is soon exceeded and the best extinguishing power may even be applied to a completely wrong area where no seat of fire exists at all. Dimensioning the system for such a large area in practice leads to impossible water quantities and pipe sizes. Alternatively, the system may be triggered a complete zone at a time, but for the selection of the right zone it is necessary to have an advanced detection system in addition to the extinguishing system. These problems are fairly well avoided in the apparatus disclosed in specification WO 0126742 (FI patent 108216). The object of the present invention is to further develop the method and system according to the prior-art solution, especially in connection with firefighting in tunnels.